Iron powders mixed with a thermoplastic resin are particularly suitable for manufacturing magnet cores, as is described in European Patent No. 0 765 199. In particular, this publication provides for an iron powder being initially treated with phosphoric acid and then mixed with a thermoplastic resin. This mixture is pressed at a temperature less than the glass-transition temperature or the melting point of the thermoplastic resin, and the pressed product is heated to cure the thermoplastic resin. The resulting components can then be annealed at a temperature greater than the curing temperature of the thermoplastic resin.
In addition, the publication describes the addition of polyetherimide and oligomers to the thermoplastic material. The polyetherimide is known under the trade name Ultem®, and the oligomers, which are described in PCT International Patent Application No. WO 95/33589 and marketed by Elf Atochem, France, are known under the trade name Orgasol 3501 and Orgasol 2001.
Furthermore, European Patent No. 0 765 199 provides for the iron powder being mixed with an auxiliary pressing agent or a lubricant, which can be a metal stearate, a wax, a paraffin, a natural or synthetic fat derivative, or an amide-type oligomer (oligoamide). The products Kenolube® from the company Höganäs AB, Sweden, H-wax® from the company Höchst AG, Germany, and Promold® from the company Morton International, Cincinnati, USA, are specifically described as lubricants or auxiliary pressing agents, which can be mixed with the iron powder at a weight percentage of 0.2 to 0.8.
Additionally, European Patent No. 0 765 199 describes pressing this starting mixture at a pressure of 400 to 1800 MPa, and subsequently annealing it in air at temperatures between 100° C. and 600° C., particularly 200° C. to 500° C.
A powdery, soft magnetic material manufactured according to European Patent No. 0 765 199 is marketed by the company Höganäs AB, Sweden under the trade name Somaloy™ 500 and is characterized in detail in the company newspaper SOMALOY™500, SMC 97–1, pages 1–11, Höganäs AB, Sweden.
In addition, such soft magnetic composites are also described in “Weichmagnetische Verbundwerkstoffe für Elektromotoren” (“Soft Magnetic Composite Materials for Electric Motors”), Jan Tengzelius, Hagener Symposium volume of minutes, Dec. 1, 2000, pages 211 to 227.
The object of the present invention is to provide a method for manufacturing a pressed part from a powder mixture that includes an iron powder that is specially used as a magnet core for common-rail injectors and has mechanical and magnetic properties that are improved in comparison with the related art.